The below-mentioned patent documents propose using aerial surveying technology to make a judgment or the like as to whether or not a fixed asset has been changed. Conventionally, there has been proposed a method in which a high-resolution image or digital surface model (DSM) data is acquired from an aircraft or the like at two different time points, and those pieces of data of the two time points are compared to each other for each pixel, to thereby judge whether or not a house has been changed between the two time points.
Specifically, in house change judgment which uses an image photographed from an aircraft or the like, registration is performed between a previously-acquired image and a newly-acquired image to obtain a difference in pixel data, such as brightness value, between the old and new images with regard to pixels at the corresponding positions, and the difference is compared to a predetermined threshold, to thereby judge whether or not there is a variation. Then, based on a group of pixels with variation, a region with variation of the image is extracted, and it is judged whether the house change is disappearance of or new construction of a house, for example.
Further, in house change judgment which uses a DSM, for example, a plurality of aerial images taken from different flight points are matched to one another, and based on differences in how the same feature looks among the plurality of aerial images, the height of the feature is obtained, to thereby generate a DSM. Then, in the same manner as in the above-mentioned comparison between the old and new images, the old and new pieces of DSM data are compared to each other for each pixel to extract a region with variation of the DSM, and then, based on the region with variation, a judgment is made as to the house change.    Patent Document 1: JP 2004-117245 A    Patent Document 2: JP 2007-3244 A